Force transducers embodying thin film strain gage resistance bridges have been in use for many years. Typically, the gages are provided on a flexure element which deforms in response to an applied force. In such cases, temperature effects may cause unequal expansion of the legs of the bridge even when no actual force is being applied. This causes a shift in the zero point of the bridge since an output will be produced even when no force is applied. Similarly, temperature effects may result in differential changes in the elasticity or spring constant of various parts of the transducer, so that a given deflection of the flexure element will cause different bridge outputs as the temperature varies. This causes a shift in the span of the bridge, also known as the gage factor or sensitivity.
Various approaches to compensation for temperature effects have been followed in the past. Bodner et al disclosed in U.S. Pat. No. 2,930,224 a type of temperature compensating strain gage in which a strain-insensitive thermocouple is used to generate a current flow opposite to that flowing in the gage resistance in order to cancel out temperature effects. The temperature compensating elements, however, are located on the strained portion of the flexure element and therefore in fact are subject to resistance variations due to applied strain. Starr also disclosed in U.S. Pat. No. 3,034,346 a technique for compensation of strain gage nonlinearity in which the compensating resistances are placed on the strained portion of the flexure element. Billette et al shown in U.S. Pat. No. 3,886,799 a type of semiconductor pressure transducer in which compensating elements are provided on the flexure element with the strain gage bridge.
While these prior art devices have achieved a measure of success in compensating for temperature effects, the location of the compensating elements on the strained portion of the flexure element causes resistance variations due to strain which tend to interfere with the desired function of the compensating elements: the minimization of temperature effects. Moreover, due to the complicated procedures by which prior art thin film strain gage transducers have been made, manufacturing time has been rather long and cost high.